The preparation of cellular polyurethanes by reacting organic isocyanates with polyols containing reactive hydrogen atoms, as determined by the Zerewitinoff reaction, is well-known in the art. These reactions are conventionally carried out in the presence of tertiary amine catalysts or organo-tin catalysts or mixtures of these.
In known formulations particularly for the preparation of flexible polyurethane foams, water is included in the formulation for reaction with part of the isocyanate thereby releasing carbon dioxide gas which acts as a blowing agent. The blowing reaction is promoted by the presence of tertiary amine catalyst. A tin catalyst is also included in the formulation to promote the isocyanate-polyol reaction. Typical various organotin compounds employed or proposed for use as catalysts or co-catalysts in urethane-forming reactions are disclosed, for example, in U.S. Pat. Nos. 3,582,501; 3,836,488; 4,119,585. U.S. Pat. No. 3,392,128 discloses the use of dibutyltin sulfonamide and U.S. Pat. No. 3,980,579 discloses a number of dialkyltin thio carboxylates.
One of the problems encountered in the use of organotin compounds previously employed in polyurethane formulations, is that these organotin compounds hydrolyze in the presence of water with resulting loss in catalytic activity. The problem is particularly evident in commercial formulations wherein a pre-mix composition is prepared and stored, including all of the components except for the isocyanate which is later added to effect the desired polyurethane reaction. This problem has been recognized in U.S. Pat. Nos. 4,032,468 and 4,043,949 wherein the use of certain organotin compounds are proposed which are claimed to be stable against hydrolysis. These patents disclose triorganotin compounds such as methyl or methoxymethyl tin halides and oxides; and certain methyl, allyl, phenyl or benzyl tin compounds in the form of their halides, carboxylates, sulfides, mercaptides, dithiocarbamates or mercaptocarboxylates.